Transverse Spin Physics

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Transverse Spin Physics
Akio Ogawa 2008 May 20 BNL Physics
Colloquium BNL
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Contents

• Introduction to Nucleon Structure
• Spin puzzles
• Results from RHIC-STAR-FPD
• Results from KEKB-Belle
• Future STAR-FMS and Beyond
• Summary

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Nucleon
Nucleon is made of 3 quarks Nucleon mass
1GeV Quark mass 0.001 0.01GeV 99 of
nucleon mass is generated by strong
interaction Quarks are moving in relativistic
speed

• Nucleon spin is ½
• Quark spin is ½
• Text book SU(3) exercise gives
• proton? 2 u? u? d?
• - u? u? d?
• - u? u? d?
• Quark spin carrying all nucleon spin

Nucleon Spin
Quark Spin
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Quark Distribution Function
Deep Inelastic Scattering (DIS)
High energy lepton
Q2
Momentum Fraction x pquark / pnucleon Resolutio
n of the probe Q2
xpnucleon
pnucleon
Quark Distribution Function q(x) Probability
of finding a quark at Momentum fraction x in
nucleon
If nucleon is made of just 3 quarks
x
0.3
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Quark Distribution Function
Deep Inelastic Scattering (DIS)
High energy lepton
Q2
Momentum Fraction x pquark / pnucleon Resolutio
n of the probe Q2
xpnucleon
pnucleon
Quark Distribution Function q(x) Probability
of finding a quark at Momentum fraction x in
nucleon
If nucleon is made of 3 quarks interacting with
gluons
x
0.3
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Quark Distribution Function
Deep Inelastic Scattering (DIS)
High energy lepton
Q2
Momentum Fraction x pquark / pnucleon Resolutio
n of the probe Q2
xpnucleon
pnucleon
Quark Distribution Function q(x) Probability
of finding a quark at Momentum fraction x in
nucleon
valence quarks
seq quarks
If nucleon is made of 3 valence quarks and sea
quarks
x
0.3
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Perturbative QCD Factorization
hadron
lepton
F
Hard Scattering xsection Calculable in pQCD
Fragmentation Function
Distribution Function
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pQCD, Factorization Universality
hadron
F
Hard Scattering xsection Calculable in pQCD
Fragmentation Function
Distribution Function
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Quark and Gluon Distribution Function
Hadron Collision
High energy quark
Q2
Momentum Fraction x pgluon / pnucleon Resolutio
n of the probe Q2
xpnucleon
pnucleon
Quark Distribution Function q(x)
Gluon Distribution Function g(x)
If nucleon is made of 3 valence quarks and sea
quarks and gluons
x
0.3
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Quark and Gluon Distribution Function
Gluon DF cannot keep rising forever
50 of nucleon momentum is carried by
quarks 50 is by gluons
Unpol PDF
CTEQ6M
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The Nucleon Spin Puzzle
Polarized Quark Distribution Function Dq(x)
q?(x) q?(x) q?(x) q?(x) Difference in
probability finding a quark with spin parallel
and anti-parallel to nucleon spin
_
_
1988 EMC
Only 20 of nucleon spin is carried by quark
spins
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The Nucleon Spin Puzzle
arXiv0804.0422v1
Spin Sum Rules 1/2 1/2 ?? ?G LL
0.2
Experiments at RHIC, CERN, DESY Recent results
from RHIC suggests Its small or even
negative? (-0.08 from a fit shown above)
Orbital Angular momentum may be playing big role
here???
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Another Spin PuzzleSingle Transverse Spin
Asymmetry (AN) in hadron collisions

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Sivers Effect
Phys Rev D41 (1990) 83 43 (1991) 261
Correlation between nucleon spin and parton kT
Related Twist-3 quark-gluon correlation at
initial state
QCD Lens Model
If there is no orbital angular momentum, Sivers
effect would be zero!
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Transversity and Collins Effect
Nucl Phys B396 (1993) 161
Transversity (quark polarization) asymmetry in
the jet fragmentation
Related to Twist-3 quark-gluon correlation at
final state
Artru model
Collins FF can be used as a probe for Transversity
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Perturbative QCD expansions
Q2 gtgt 1 as(Q2)0.2
Collinear factorization
s(x,Q2) s2(x,Q2) T2(x,Q2) O(as)
O(as2)
1/Q
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The Nucleon Spin Puzzle
Spin Sum Rules
Longitudinal 1/2 1/2 ?? ?G LL
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RHIC - First and only Polarized pp Collider
RHIC pC Polarimeters
Absolute Polarimeter (H? jet)
BRAHMS PP2PP
PHOBOS
Siberian Snakes
Siberian Snakes
PHENIX
STAR
Spin Rotators (longitudinal polarization)
Spin Rotators (longitudinal polarization)
Pol. H- Source
LINAC
BOOSTER
Helical Partial Siberian Snake
AGS
200 MeV Polarimeter
AGS pC Polarimeter
Strong AGS Snake
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STAR Detector and Physics
Run6 TPC -1.0 lt ? lt 1.0 FTPC 2.8 lt ??? lt
3.8 BBC 2.2 lt ??? lt 5.0 EEMC 1 lt ? lt 2 BEMC
-1 lt ? lt 1 FPD/FPD ? 3.3 4.1
FPD engineering test of the Forward Meson
Spectrometer
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STAR Forward Pion Detector (FPD)
Run6 TPC -1.0 lt ? lt 1.0 FTPC 2.8 lt ??? lt
3.8 BBC 2.2 lt ??? lt 5.0 EEMC 1 lt ? lt 2 BEMC
-1 lt ? lt 1 FPD/FPD ? 3.3 4.1
FPD engineering test of the Forward Meson
Spectrometer
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Why forward in hadron collider interesting?
p0
Ep
qq
EN
p/d
qp
p/Au
xgp
xqp
qg
EN
(collinear approx.)

• Large rapidity p production (hp4) probes
  asymmetric partonic collisions
• Mostly high-x valence quark low-x gluon
• 0.3 lt xqlt 0.7
• 0.001lt xg lt 0.1
• ltzgt nearly constant and high 0.8
• Large-x quark polarization is known to be large
  from DIS
• Directly couple to gluons A probe of low x
  gluons

NLO pQCD S. Kretzer
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Measurements at STAR FPD
PRL 92, 171801 (2004)
vs200 GeV, lt?gt 3.8
Asymmetry revealed at lower energies persists at
vs200 GeV
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p0 AN at vs200 GeV xF-dependence
Submitted to PRL arXiv0801.2990v1 hep-ex
AN at positive xF grows with increasing xF Fits
to SIDIS (HERMES) is consistent with data
U. DAlesio, F. Murgia Phys. Rev. D 70, 074009
(2004) arXivhep-ph/0712.4240
C. Kouvaris, J. Qiu, W. Vogelsang, F. Yuan,
Phys. Rev. D 74, 114013 (2006).
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AN(pT) in xF-bins
Submitted to PRL arXiv0801.2990v1 hep-ex
Measured AN is not a smooth decreasing function
of pT Sign of Sivers Collins mixture? -gt
Need to separate Sivers from Collins effect
U. DAlesio, F. Murgia Phys. Rev. D 70, 074009
(2004) arXivhep-ph/0712.4240
C. Kouvaris, J. Qiu, W. Vogelsang, F. Yuan,
Phys. Rev. D 74, 114013 (2006).
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The Nucleon Spin Puzzle
Spin Sum Rules
Longitudinal 1/2 1/2 ?? ?G LL
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Belle _at_ KEK-B factory

• KEKB
• Asymmetric collider
• 8 GeV e- 3.5 GeV e
• Ös 10.58 GeV , ee- ? ?(4S) BB
• Off-resonance 10.52 GeV
• ee- ? qq (u,d,s,c)
• Integrated Luminosity
• 547 fb-1 (on resonance)
• 60 fb-1 (off-resonance)

World best luminosity at right energy!
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(No Transcript)
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Unlike and Like sign pion pairs
Hfavored
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Complication Gluon Radiative Contribution
Gluon radiation gives same cos(F1F1) dependence
as Collins effect
But its independent from Unlike / Like sign pair
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Published Collins Asymmetries
Phys.Rev.Lett.96232002,2006
Off-resonance Data (29fb-1)
U/L U/C
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Preliminary Collins Asymmetries
Submitted to PRD arXiv0805.2975
On-resonance Data (547fb-1)
PRELIMINARY
U/L U/C
Large Collins-FF2 is observed!
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First QCD Analysis of SIDIS ee- !
Anselmino, Boglione, DAlesio, Kotzinian, Murgia,
Prokudin, Turk Phys. Rev. D7505032,2007
Fit includes
HERMES SIDIS
COMPASS SIDIS
Belle ee-(published)
? transversity dist.
Collins FF
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The Nucleon Spin Puzzle
Spin Sum Rules
Longitudinal 1/2 1/2 ?? ?G LL
Last decade, theory and experiments developed
rapidly together
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Three Highlighted Objectives In FMS
Proposal(not exclusive)
Forward Meson Spectrometer (FMS)
hep-ex/0502040

• A d(p)Au?p0p0X measurement of the parton model
  gluon density distributions xg(x) in gold nuclei
  for 0.001lt x lt0.1. For 0.01ltxlt0.1, this
  measurement tests the universality of the gluon
  distribution.
• Characterization of correlated pion cross
  sections as a function of Q2 (pT2) to search for
  the onset of gluon saturation effects associated
  with macroscopic gluon fields. (again d-Au)
• Measurements with transversely polarized protons
  that are expected to resolve the origin of the
  large transverse spin asymmetries in reactions
  for forward ?? production. (polarized pp)

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Special universality (breaking) of Sivers
Function
DIS attractive
q
p
- Sivers pp?gjet -c Sivers
pp?jetjet
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Forward Meson Spectrometer for Run8

• FMS will provide full azimuthal coverage for
  range 2.5 ? h ? 4.0
• broad acceptance in xF-pT plane for inclusive
  g,p0,w,K0, production in pp and d(p)Au
• broad acceptance for g-p0 and p0-p0 from
  forward jet pairs to probe low-x gluon density in
  pp and d(p)Au collisions

spacers
Run-8 FMS as seen from STAR interaction point
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Forward Meson Spectrometer for Run8

• FMS will provide full azimuthal coverage for
  range 2.5 ? h ? 4.0
• broad acceptance in xF-pT plane for inclusive
  g,p0,w,K0, production in pp and d(p)Au
• broad acceptance for g-p0 and p0-p0 from
  forward jet pairs to probe low-x gluon density in
  pp and d(p)Au collisions

spacers
Run-8 FMS as seen from STAR interaction point
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Forward Meson Spectrometer for Run8

• FMS will provide full azimuthal coverage for
  range 2.5 ? h ? 4.0
• broad acceptance in xF-pT plane for inclusive
  g,p0,w,K0, production in pp and d(p)Au
• broad acceptance for g-p0 and p0-p0 from
  forward jet pairs to probe low-x gluon density in
  pp and d(p)Au collisions

spacers
Run-8 FMS as seen from STAR interaction point
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FMS Summary and Future

• Forward Meson Spectrometer (FMS) is constructed
  took data in run8!
• Low-x physics (Can we see Gluon saturation?
  CGC?)
• Separate Sivers from Collins
• Jet-like events, or pi0-pi0
• Near and away side jet-pi0 correlations
• Heavier mesons (Eta, Ks, J/psi)?

• With Future running, Direct Photon Jet to test
  sign change
• of Sivers function

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Transverse Spin Asymmetries for the DY
Processhttp//spin.riken.bnl.gov/rsc/write-up/dy-
final.pdf
Two 10-week runs in 2015 and 2016 with RHIC-II
luminosity detector upgrades (charge sign
measurement at forward)
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Conclusion

• Transverse spin provides an unique way to study
  nucleon spin structure (p)QCD itself, and its
  an essential part of present and future RHIC
  program